Up to now, image display apparatuses having various structures have been proposed. FIG. 14 is a structural cross sectional view illustrating an example of one of the image display apparatuses which have been known.
In FIG. 14, an image display apparatus 1400 includes multiple pixel structures each having a pixel 1402.
In the image display apparatus 1400, the pixel 1402 is provided on an inner surface side of a front plate 1401. The front plate 1401 is made of a medium transparent to visible light, for example, glass or plastic.
The pixel 1402 includes a light-emitting layer 1403 and an excitation unit (not shown) for exciting the light-emitting layer 1403.
The excitation unit has, for example, a structure in which an electron emitting element and an electrode are arranged on a substrate and an electrode is provided between the front plate 1401 and the light-emitting layer 1403. In such a structure, an electric field is applied to the electron emitting element to emit electrons. The electrons are injected into the light-emitting layer to generate light in the light-emitting layer.
Another example of the excitation unit has a structure in which an anode and a cathode are provided on a front surface and a rear surface of the light-emitting layer. Light generated in the light-emitting layer passes through the front plate 1401 and is extracted to an outside to serve as display light 1405.
The image display apparatus is required to be high in contrast and less influenced by an ambient environment. In order to improve the contrast of the image display apparatus in bright light, it is necessary to increase display luminance.
In order to increase the luminance of the display light in the image display apparatus 1400, it is important to reduce a loss occurring while the light generated in the light-emitting layer 1403 is extracted to the outside.
One of factors of the loss is a total-reflection loss at an interface between the light-emitting layer 1403 and the front plate 1401 or an interface between the front plate 1401 and an outside region.
When light propagates from a high-refractive index medium (light-emitting layer 1403 or front plate 1401) to a low-refractive index medium (outside region), light propagating at an angle larger than a critical angle is totally reflected and confined in the high-refractive index medium.
The totally reflected light is not extracted to the low-refractive index medium and propagates through the high-refractive index medium, to thereby cause the loss.
A method of providing a fine structure between layers made of media having different refractive indices has been proposed as a method of reducing the total-reflection loss to increase the luminance of the display light.
For example, an image display apparatus (organic electroluminescence display apparatus) illustrated in FIG. 15 is described in PTL 1.
An image display apparatus 1500 illustrated in FIG. 15 includes a front plate 1501, a transparent electrode 1502, a light-emitting layer 1503, and an electrode layer 1504. A fine structure 1505 is provided between the front plate 1501 and the light-emitting layer 1503.
The fine structure 1505 has a refractive index distribution having a period equal to a wavelength of light in a plane parallel to the front plate.
Light 1509 generated in an inner portion of the light-emitting layer 1503 is diffracted to reduce light 1511 propagating at an angle equal to or larger than a critical angle, to thereby increase light 1510 propagating at an angle smaller than the critical angle. Therefore, the light extracted to the outside is increased to improve the display luminance.